Millions of Americans have been told to prepare for a possible tornado outbreak on Tuesday. 

Meteorologists warned that severe thunderstorms are expected from the southern Plains into the southern Great Lakes vicinity starting between 4pm and 6pm CT.

The states currently at risk include Illinois, Indiana, Missouri, Iowa, Texas, Oklahoma, Michigan, Ohio, Wisconsin and Tennessee. 

'All severe hazards are possible, including the risk for a few strong to intense tornadoes and very large hail,' the Storm Prediction Center (SPC) said in a statement.

Residents across the entire area at risk for severe weather should identify the safest place to shelter at home, work or school in the event a tornado occurs, AccuWeather noted.

In all, nearly 80 million people are at risk from some form of severe weather on Tuesday, the SPC warned. 

The greatest risk for tornadoesis centered across northern and central Illinois, extending into northwest Indiana. 

Meteorologists have issued a Moderate Risk, the second-highest level on the agency’s five-tier scale, for this region, warning that conditions could support multiple strong to intense tornadoes. 

Forecasters say a powerful low-level jet strengthening late in the afternoon and evening will combine with warm, moisture-rich air and strong wind shear to create a highly favorable environment for rotating supercell thunderstorms. 

AccuWeather senior meteorologist Adam Douty said: 'This could be the largest outbreak of severe weather so far this year.' 

Tornadoes in northern and central areas could reach EF2 or EF3 strength, meaning winds could exceed 110 miles per hour. 

While severe weather is also possible across parts of Texas, Oklahoma and the southern Plains, forecasters say the most dangerous conditions for significant tornadoes are expected in Illinois and nearby areas of Indiana. 

These regions are under an Enhanced Risk, meaning severe storms are likely, but the chances of the most dangerous tornadoes are lower than in Illinois.

Storms developing along a dry line in west Texas could produce very large hail,  potentially larger than golf balls, during the afternoon and early evening before evolving into lines of storms capable of producing widespread damaging winds.

Parts of central Texas and southern Oklahoma could also see a few tornadoes, especially where moisture levels are higher. 

AccuWeather meteorologist Alex Sosnowski said: 'Regardless of whether or not the event will reach tornado outbreak proportions, all it takes is one tornado to strike a populated area, leading to multiple casualties.

'People should take the upcoming 'severe weather outbreak' threat seriously.' 

Later in the evening and overnight, storms are expected to grow into larger clusters and move east across the Midwest and Ohio Valley. 

Even as the storms merge together, damaging winds and tornadoes could continue as they track across the region. 

Additional storms may develop from Oklahoma and Kansas into Missouri later tonight, where rotating thunderstorms could again produce hail, damaging winds and isolated tornadoes before moving eastward early Wednesday. 

People living in the areas under threat are being urged to stay alert and make sure they have multiple ways to receive weather alerts, especially as storms could continue after dark. 

Forecasters warn that tornadoes developing at night can be particularly dangerous because many people are asleep and less likely to receive warnings in time. 

According to the National Oceanic and Atmospheric Administration, tornadoes that strike overnight are about twice as deadly as those that occur during the day.